1. Field of the Invention
This invention relates to one-way drive, overrunning clutch mechanisms, and more particularly to an improved lightweight, one-way clutch of simplified construction and high torque transmitting capability which is especially well adapted for high speed operation.
2. Description of the Prior Art
One-way drive overrunning clutch mechanisms, hereinafter generally referred to as clutches, or as overrunning clutches, are well known and widely used in a variety of applications ranging from low speed devices such as bicycle drives to high speed mechanisms such as automotive transmissions and torque converters. Commercial clutches employed in high speed automotive transmissions have in the past generally been of the sprag-type or the roller-ramp type, both of which depend on a wedging action to lock up, or to transmit torque between the driving and driven members of the clutch. The wedging action of these clutches produces extremely high stresses in component parts, and the clutches are relatively heavy and expensive to manufacture. Such clutches generally are considered the weakest link in an automatic transmission.
Clutches are also known which employ rigid struts positioned between the driving and driven clutch members, or clutch plates, for pivotal movement between a driving position engaging shoulders defined by notches in the driving and driven clutch plates to transmit torque therebetween upon relative rotation in one direction and to permit overrunning, or free wheeling, upon relative rotation in the opposite direction. Clutches of this type are disclosed, for example, in U.S. Pat. Nos. 5,070,978 and 5,449,057.
In the typical strut-type clutch, the individual struts are mounted for pivotal movement between a driving position in which opposed ends, or opposed edges of at least one strut engages a shoulder formed by notches in closely spaced, opposed faces of the driving and driven clutch plates upon rotation of the driving member in one direction and a retracted position in which the struts are out of engagement with at least one of the clutch plates when the driving member is rotated in the opposite direction relative to the driven member. The struts may be pivotally mounted on a carrier disposed between the clutch faces as in U.S. Pat. No. 5,449,057, but in most commercial drives of this type, the struts are carried in a pocket in one clutch plate face with one end or edge continuously contacting a shoulder defined by the pockets. Whether supported by a carrier or mounted in a pocket in one of the clutch faces, the individual struts are continuously urged to a position to engage both clutch faces by a resilient member, typically a spring, to thereby lock the two clutch plates together upon rotation of the drive member relative to the driven member in one direction. Upon relative rotation in the opposite, or overrunning direction, the spring members continue to urge the struts into contact with the clutch faces and tend to urge the struts into each of the pockets as they are rotated, with the shape of the pockets camming the struts back as rotation continues.
As suggested in the above-mentioned U.S. Pat. No. 5,449,057, the previous overrunning clutches used in high speed transmission mechanisms have required a continuous supply of lubrication to assure that the struts, sprags, or rollers are continuously coated to minimize wear, particularly when the clutch is operated in the overrunning mode. When such clutches are employed in mechanisms such as automatic transmissions containing a reservoir of lubricant which is continuously splashed throughout the interior of the mechanism by the various rotating components, this more or less random distribution of lubricant has been relied upon to lubricate the clutches. It has been discovered, however, that such systems do not always provide adequate lubrication to minimize wear and to enable the most efficient operation, especially in the overrunning mode.
It has been shown that pivotal movement of the struts of strut-type clutches can be effectively damped at high speeds by maintaining the struts submerged in a bath of lubricating oil so that they remain essentially stationary in the overrunning mode. This substantially eliminates rapid depression and expansion of the resilient spring members engaging each strut as the strut passes over the respective recesses in the adjacent clutch face and thereby greatly increases the spring life by effectively eliminating fatigue failures. Further, by maintaining the struts substantially fully submerged in a bath of lubricating oil during all high speed operations, direct metal-to-metal contact between the struts and clutch faces is avoided by the continuous coating of lubricant.
The above-mentioned U.S. Pat. No. 5,070,978 discloses the concept of providing a housing, with seals between the housing and input shaft, to enclose the clutch plates. The sealed housing is filled with oil to assure continuous lubrication to "float" the two opposed clutch plates away from one another during free wheeling or overrunning. This patent also seems to recognize, at column 8, lines 10-12, that filling the housing with oil may have an effect on strut movement during overrunning at high speed, although the patent also states that the struts "hardly move at all" at high speeds even without filling the housing with oil. The housing comprises a generally cup-shaped, output shell having an open end which is closed by a threaded closure plate. The use of a separate housing and threaded closure greatly increases the cost of the clutch, and presents the potential for failure in the event of the threading connector becoming loose during prolonged use. Further, no provision is made for replenishing the oil supply in the event of seal failure, thereby presenting the potential for excessive wear, overheating and eventual failure of the clutch in the event of oil escaping from the sealed housing. The sealed housing would act as a shield effectively preventing splashed oil from reaching the struts in the event of seal failures. Further, the separate housing and threaded closure greatly increases the overall weight and size of the clutch assembly.
Accordingly, it is an object of the present invention to provide an improved lightweight strut-type overrunning clutch assembly having improved means for assuring continuous lubrication for the clutch components.
Another object is to provide such a clutch assembly which assures that the movable struts are continuously submerged in a reservoir of oil during high speed operation regardless of the attitude of the mechanism in which the clutch is used.
Another object is to provide such a clutch assembly having an improved lightweight retaining means retaining the clutch plates in assembled relation and providing an oil-tight joint with one of the clutch members and serving as a weir or dam to retain a reservoir of oil under pressure from centrifugal force between the clutch plates and enveloping the struts and spring members during high speed operation.
Another object is to provide such a clutch assembly including means for providing a continuous flow of oil through the clutch assembly during operation.
Another object is to provide such a clutch assembly which is less expensive to manufacture and which is highly reliable in operation.